TargetTalk

what is the purpose of bedding a rifle

This is actually a profound question - I hope it stimulates an erudite discussion. There is a lot of misinformation around concerning bedding and other technical issues. There's a lot of information to be found on the 'net, but a lot of it is suspect, and some of it is quite wrong: be careful!

After that, I feel rather diffident about trying to answer, but here goes...

The term 'bedding' covers several methods of providing a secure mechanical coupling between the rifle's action and the stock. Wooden stocks can swell and shrink with changes in the water content of the wood. This can alter the force between action and stock provided by the screws attaching action to stock. Sometimes only the receiver is 'bedded' to the stock, sometimes the 'bedding' extends some way along the barrel.

The purpose is to provide a consistent coupling between those parts of the rifle which tend to vibrate and the supposedly 'dead' stock. If the barrel vibrates differently from shot to shot, the group size will suffer. It is considered best if the bullet leaves the barrel at the muzzle's maximum deflection as it vibrates. At this point, as the muzzle changes from moving in one direction to the other, its velocity will be zero, therefore no sideways velocity component is added to the bullet's trajectory. This obviously requires that the time the bullet takes to travel the length of the barrel results in it exiting at the time of maximum barrel deflection, so it is clear that accuracy requires consistent bullet velocity provided by the ammunition. High-grade target ammo is characterised by a small spread in muzzle velocity.

What if the bullet velocity is consistent, but it exits whilst the muzzle is moving? Well, you can't do much fine tuning of velocity, although you will find different ammo brands and batches will alter the bullet exit and muzzle movement relationship. It's more sensible to try to alter the way the barrel vibrates, and this is what barrel 'tuners' do. They add mass to the muzzle end of the barrel, and can be moved along the barrel, thereby altering its vibration characteristics.

The coupling between action and stock has a considerable effect on barrel vibration. This is evident when the tightness of the action mounting screws on, for example, an Anschutz rifle is altered. Minimum group size will be found to occur at one particular screw torque. It's obviously important that what lies between the action and the head of the screw is as consistent as possible, and this is achieved by the application of one of the various 'bedding' methods. Commonly used is a filled epoxy medium which fills all the little voids between stock and action (or whatever parts are bedded), but alloy pillars are also commonly let into wooden stocks, and the action secured to them.

I think there's rather more art than science often applied to bedding. I hope others will contribute, as this is only scratching the surface.

Excellent answer to a very intersting question!

I would only offer the following: Bedding the action to the stock "generally" only provides noticeable benefit to "high power" (center fire at least) "long range" (200m and beyond) rifles.

The amount of improvement in precision becomes somewhat a matter of argument and/or faith when dealing with the international competition equipment (.22LR target-barreled match rifles) and courses of fire (distances within 100 meters).

I know, I know, every little bit helps . . . and action bedding has become somewhat of a "standard must have" for competition rifles . . .

Steve Swartz

i have always considered bedding a way to make the action sit the same way in the stock every time you torque your bedding screws. It's pretty much just a better fit than an action straight on the wood stock.

In terms of the vibrations, it's the consistency again that you're looking for. I've had my rifle bedded for some time and when I switched ammo lots, I found through testing that I needed to increase my torque setting from 31 inch pounds (3.5Nm) to 35 (3.9Nm) to get the best groups. In smallbore, it's hard to see the benefit because it is usually measured in a mm or 2 at best at 50m. But as stated above, every little bit helps when your 10 ring is only a cm.

So if say I have a stock Kimber 82G that shoots consistent high 220's and low 230's on usbr target and was thinking of buying a tuner I should also have the action bedded if not part of the barrel also? I suspect I should try to get the trigger as light as possible as it is still set as recieved with no adjsutments. I shoot this rifle as well as my 11 yr old daughter who also shoots mid to high 220's with it. We shoot Sk StandardPlus but have tried eley black box and laupa master L the sk groups the best.

[quote="Steve Swartz"]The amount of improvement in precision becomes somewhat a matter of argument and/or faith when dealing with the international competition equipment (.22LR target-barreled match rifles) and courses of fire (distances within 100 meters).[quote]

Interesting statement. Can't say that I agree, but interesting.

What makes you believe that bedding a .22 is not beneficial for international competition equipment?

Perhaps Mr Swartz means that competition .22 rifles are pretty well 'bedded' straight from the box, whereas hunting-type rifles often leave a lot to be desired, and it is those that mainly receive aftermarket bedding attention. The forces between action and stock are much greater in a high-powered rifle, compared to a little .22, so greater benefit may be expected from the provision of good coupling between action and stock. However, it is common knowledge that altering the characteristics of the coupling between action and stock (in otherwords whatever passes for 'bedding') can have a very great effect on the group size obtained with a competition .22 rifle.

2.5 points:

1. Match grade competition .22LR guns have stiff barrels, tight actions, and are already seated rigidly in the stock. The designs "out of the box" are pretty much ready to go. Paying someone to re-bed the action is a waste of time (and the re-bedding may end up being worse than the factory configuration). Mfgrs who offer bedding as an "upgrade option" are just trying to fluff up their profit margins.

1.5. Harmonics are not a significant sourc of error in match-grade .22LR target guns.

2. Much of the testing I have seen to support claims of "improvement" are bogus. Shooting a five shot group and measuring the ES is not a reliable way to assess the accuracy/precision of a given treatment.

The issue reminds me of people who spend a lot of time finding the right "brand" of ammo when
a) the lot-lot variation within a brand is often wider than the brand-brand variation across lots; and
b) the testing is done using ES of 5-shot groups (using only 1 group per test treatment

Anyhow

The bottom line is this: if it gives you more confidence in your equipment, and allows you to concentrate on TRAINING your TECHNIQUE then it is well worth the investment!

I was never much into the science behind it, but years ago I was way into benchrest with light weight hunter rifles. It was very common to see improvement in group size after glassbedding the original woodstock. I became quite good at bedding 725, 722, 721, M70, Sako rifles. By todays standards in benchrest though, I could not compete.

Although I do not compete in .22 at an international level, I do own a Winchester 52E, and it is 'glass bedded, from the factory. It is consistent, and is not affected by temperature of humidity changes, as a wood stocked gun may be that is not bedded.

From the POV of .22 target rifles, my Anschutz 1913 Supermatch beds directly to the wooden stock (unless there's some super-thin coating around where the action beds down). This is the same for every other .22 target rifle I have come across (Annie, FWB and Walther) - wood or alustock, the action just drops right into the machined hole in the stock.

I think the main thing to remember with competition rifles is:

(a) A basic competition rifle will be more expensive than a basic hunting rifle (An Annie 1907 costs 3-4 times as much as an entry level CZ). Thus it can be expected that the finish (and bedding) will be superior right out the box. As a result, after-market work will show much more benefit on a sporting rifle than a competition rifle

- The caveat is that fullbore rifles are a different kettle of fish thanks to the much greater strains placed on the system (a 7.62mm action typically copes with a breech pressure of 20 tonnes per square inch, which goes up to 23-24TSI if you get your rifle wet such that the breech forms a "wet" seal).
- One must also bear in mind that, even after an ISSF course of fire (60 shots, 75 mins) a .22 barrel will not really be much warmer to the touch than when you started. A fullbore barrel by comparison will be noticeably warmer after just a few shots. If bedded directly to wood, that heat could cause warping, etc. It needs to be bedded to a material that will not shift with temperature. The smaller forces and negligible heat-build-up mean bedding is far less critical for a .22.

(b) A .22 target rifle is likely going to be shot indoors, or if outdoors, often from a covered firing point (in the UK at least). It comes out the box, shoots, goes back in the box, gets TLC when it gets home if conditions were poor, and then goes into a cabinet in a part of the house where the temperature and humidity are stable. Compare that to a hunting rifle, which may be out in the woods or fields in all conditions - hot, cold, wet, dry. They have to deal with much more variable conditions.

Hemmers wrote:
(b) A .22 target rifle is likely going to be shot indoors, or if outdoors, often from a covered firing point (in the UK at least). It comes out the box, shoots, goes back in the box, gets TLC when it gets home if conditions were poor, and then goes into a cabinet in a part of the house where the temperature and humidity are stable. Compare that to a hunting rifle, which may be out in the woods or fields in all conditions - hot, cold, wet, dry. They have to deal with much more variable conditions.

I would argue that moving between geographic areas in the USA, the temperature and humidity will change quite a bit, and I am willing to be that one will find that the torque on the bedding screws will vary as the stock (wood) shrinks or expands. I believe that a good bedding job will only insure consistency.

Indeed, and that's one of the reasons given for alloy stocks. However, alloy and steel have different coefficients of expansion, so one wonders at the wisdom. Whatever, target shooters get pretty obsessional about screw torque.

Interesting question, and I think this is a often overlooked aspect of precision rimfire shooting.

In benchrest, be it centerfire or rimfire, bedding is one of the most important things to do correctly, but unfortunately few people study bedding or do it enough to have all the details worked out.

Unfortunately, there is a tremendous amount of information that involves bedding, and there are two distinct schools of thought: Traditional bedding or Glue-ins.

Bedding, when executed properly and with enough cure time, layering of coats, action binding relief, and uniform density of materials will (in my opinion) deliver a more consistently accurate rifle day to day.

Errors in bedding, or lack there of, are often missed and incorrectly labeled as bad ammo, fliers, hold error, optics error for the BR guys, wind gust, ect.

Shooting Kiwi wrote:Indeed, and that's one of the reasons given for alloy stocks. However, alloy and steel have different coefficients of expansion, so one wonders at the wisdom. Whatever, target shooters get pretty obsessional about screw torque.

I had a Win. 52C that I glass bedded in a very heavy thumbhole laminated stock. I would always loosen the action screws after a match and then tighten them just before shooting. One time at a prone match in Dauphin, PA I was distracted and forgot to tighten them. Our first match was at 100 yds. and I shot all forty rounds before I realized what I did. I didn't notice any unusual grouping at all. The bedding job was very tight, but the screws were VERY loose.
After that I didn't get as obsessed about screwing. I mean screw torque.
Ben